The proposed research is designed to study the long term consequences of being exposed to psychosocial stress (episodic vs. chronic) during infancy using a well controlled nonhuman primate model. It is based upon two recent findings from this laboratory's mother-infant (m-i) research program. First, we have found that squirrel monkey infants that had experienced repeated brief m-i separations prior to weaning displayed an earlier onset of puberty and a reduced biobehavioral response to the stress of social isolation when examined as juveniles. Second, we have established a paradigm that produces chronic stress that can be imposed m-i squirrel monkey dyads to study the long term effects of chronic stress during infancy. Increasing the difficulty to obtain food (without restricting the amount of food consumed) resulted in chronic elevation of plasma cortisol levels in both mother infants, and disruption of social relationships. The specific aims of this proposal are: 1) To assess the long term consequences of exposure to the acute and episodic stress of repeated m-i separations. We will investigate whether these effects are simply a response to removal from the mother or whether the degree of the stress associated with the separation is important. The length of separation and the environment into which the infant is placed following separation will be varied in ways that have been shown to increase or decrease the indices of stress. In addition to studying the undisturbed behavioral and physiological development of these differentially-reared monkeys, we will assess their biobehavioral responses to a variety of psychosocial stimuli (e.g., social isolation, exposure to a novel stimuli in the home cage, placement in a novel environment alone or with unfamiliar conspecifics) beginning at weaning and continuing through early adulthood. 2) To investigate the long term consequences of exposure to chronic stress during infancy. Specifically, this study will assess the long term effects of the stress associated with being reared under conditions of increased difficulty to obtain food. These offspring will be subjected to a similar battery of tests as referred to above. 3) To examine the interaction of the acute stress of m-i separation with the chronic stress of increased difficulty to obtain food. In addition to determining the long term consequences of being separated under a chronic stressful environment, this study will examine the immediate response of the m-i dyad to the challenge of brief separation and its subsequent effect on the m-i relationship upon reunion under conditions of chronic stress.